Hi "anonymous" why do you want to hack his account? If your looking to find information about certain things....You might not like what you find. Annnnd if you don't find anything and your husband finds out that you did that....well....your not gonna much of marriage anyway. Why not sit down and talk with him like an adult? If you can act like an adult about whatever it is you seek to find out, he may just tell you if asked. Respect the privacy.
Now why would you want to do that? What for?
Hacking anyone's account is illegal and immoral, even (or especially) if the account belongs to your husbands. There are definitely ways to hack his account, though you may want to read up on the repercussions of getting caught before you do anything.
Here's a good video to watch before you read any further:
Yes, the story above is referring to a hacker that targeted celebrities, but I can tell you that law enforcement are looking to crack down on the hacking phenomenon - and if your husband becomes suspicious that has accounts have been compromised, what's to say he won't go to the police?
Why you should think carefully about hacking your husband's account
I'm not sure why you think he has something to hide but there are ways of finding out if that is the case without hacking his account. If he finds out (and he probably will) what state will that leave your marriage in?
Most partners are open with each other and know each others passwords etc. Most of my friends have access to their husband/partners accounts and can see anything he does. Maybe you could tell your husband this, offer to share your password with him (it has to work both ways) and wait for his reaction. If he has something to hide he won't want to do that.
If that is the case then you have a right to know why, so it will be a good conversation starter and a time for him to tell you if there is something going on in his life that he has been hiding from you.
Just be aware that sometimes ignorance is bliss and you may not like what you find out.